Method and apparatus for casting refractory metals



W. E. KUHN June 25, 1957 METHOD AND APPARATUS FOR CASTING REFRACTORY vMETALS Filed May 3. 1952 1li; n

55 f ll W. E. KUHN June 25, 1957 METHOD AND APPARATUS FOR CASTING REFRACTORY METALS Filed May 3. 1952 5 Sheets-Sheet 2 INVENTOR.

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W. E. KUHN `lune 25, 1957 METHOD AND APPARATUS FOR CASTING REFRACTORY METALS Filed May s. 1952 3 Sheets-Sheet 3 lVIE'I'HOD AND APPARATUS FOR CASTNG REFRACTORY METALS William E. Kuhn, Niagara Falls, N. Y., assigner to National Lead Company, New York, N. Y., a corporation of New Jersey Application May 3, 1952, Serial No. 285,869

11 Claims. (Cl. 22-69) This invention relates to metal casting and is particularly concerned with precision casting of refractory metals such as titanium and zirconium and alloys of these metals.

Because of their high melting points, their resistance to corrosion and their compartively low densities combined with high strength, titanium and zirconium are useful for making machine parts and metal elements of various kinds. Thus, titanium has been found useful for forming compressor blades for turbines or jet engines and zirconium is of interest for making dentures and inserts for cranioplasty and the like. Hitherto, however, the use of these metals and their alloys has been restrained by diiiculties inherent in their fusion and working. The casting of such metals and alloys in complicated shapes to close tolerances has not been feasible since at elevated temperatures the metals are readily reactive with the oxygen and nitrogen of the air. Moreover, at the high temperatures required for their casting, both titanium and zirconium attack the refractories ordinarily used for crucibles with consequent contamination of the metal and change of properties. At the present time ingots of reasonably high purity may be obtained by known methods and simple shapes may be formed from such ingots by forging, rolling, swaging, etc. without serious oxidation of the metals. The production of complicated shapes of high purity, however, still presents a virtually unsolved problem since their fabrication by conventional methods is extremely dicult and prohibitively expensive. lt may also be noted that in the case of many brittle alloys, forging, rolling, etc. are not possible even for the manufacture of simple shapes. Hence, a practical and convenient method for precision casting of such metals and alloys in complicated shapes and without contamination is highly desirable and fills a pressing need.

An object of the invention is to provide a method for making precision castings of refractory metals such as titanium and zirconium and alloys of such metals without contaminating the metal with impurities.

Another object of the invention is to provide a method of making castings of the character described in which fresh metal is supplied to the furnace at intervals and casting is intermittent as molds are brought into position to receive the molten metal.

A further object of the invention is to provide a method of making castings of the character described in which the metal is fused in a con-contaminating crucible and cast without removing it from the furnace.

Another object of the invention is to provide a method of making castings of the character described in which the metal during fusion and casting is protected by vacuum or by an inert protective atmosphere.

A further object of the invention is to provide a method of making castings of the character described in which the protective atmosphere used during fusion of the metal assists in obtaining accurately formed castings.

Still another object of the invention is to provide apparatus of simple and durable character which is par- 7955,644 Patented .lune 25, 1957 ticularly adapted for carrying out the method described.

Other objects and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings.

The present invention now makes it possible to produce either small or relatively large high quality castings of metals such as titanium and zirconium and their alloys with virtually no metal contamination. Moreover, the castings are of such precision as to minimize the amount of subsequent machining or grinding required. These desirable results are accomplished by fusion of the metal in a non-contaminating Crucible while excluding air therefrom and then, Without removing the fused metal from the furnace, casting into molds which may be of various materials but which have a high thermal conductivity. When intricate castings are required the invention also comprehends the use of the pressure of a protective atmosphere in the furnace for obtaining complete lling of the mold cavity.

In the drawings:

Figure 1 is a top plan view of a furnace constructed in accordance with the present invention and adapted to carry out the novel method of the invention;

Figure 2 is a fragmentary, longitudinal, vertical sectional view taken on the line 2 2 of Figure 1 Figure 3 is a transverse, vertical sectional view taken substantially on the line 3 3 of Figure 2;

Figure 4 is a fragmentary detail View showing a modilied form of mold adapted for use in forming castings according to the method of the present invention; and

Figure 5 is a fragmentary, sectional view illustrating a modification of the apparatus adapted to prevent clogging of the pouring opening.

Referring to Figure 1, it will be seen that the furnace illustrated comprises a central melting and casting portion designated generally by the reference character 11 and a pair of aligned tunnel portions 12 and 13 projecting, respectively, from the opposite sides of the central portion 11 at the bottom thereof. The tunnel 12 serves as an entrance through which molds 15, prepared for casting, may be intermittently fed into the central portion of the furnace and the tunnel 13 provides for egress of the filled molds from the furnace.

The central portion 11 of the furnace, the construction of which will best be seen from Figures 2 and 3, comprises a base plate 15 on which there is mounted a housing 17. The latter is formed with spaced walls 18 and 19 between which a liquid coolant is circulated, the coolant being admitted and withdrawn through the pipes 2t). Mounted within the housing 17, and intermediate the base plate 16 and the top of the housing, is a copper block 22, one end of which serves as a hearth for fusion of the refractory metal. The block is so formed as to have close contact with the cooled inner Wall 19 of the housing 17 and divides the interior of the furnace into an upper, fusion chamber 26 and a lower, casting chamber 27. Preferably the copper block 22 is formed as a casting and is provided with interior passages 29 for the circulation of a cooling medium such as water.

The top of the block 22 is dished With inclined side Walls. Adjacent the front of the block, parallel to the tunnels 12 and 13, there is formed a trough 23 having a pair of spaced pouring openings 24 providing communication between the fusion chamber 26 and the casting chamber 27. The pouring openings 24 are preferably enlarged at their lower ends which, as shown in Figures 2 and 3, may conveniently be conical in cross-section. Rearwardly of the trough 23 in the dished top of the copper block 22 the refractory metal is melted by arc fusion. Since the Water-cooled copper is not wetted by the molten titanium or zirconium, pickup of impurities from a melting crucible is avoided.

It will be understood that the furnace as a whole is Vintended to be pivotally supported by appropriate and convenient means (not shown) to permit it to rotate about an `axis parallel to the tunnels 12 and'13. In VFigure 3 the furnace is shown in position for ycasting molten metal while normally between pourings it occupies a position rotated about 30 in a clockwise direction from the position shown in Figure 3 with a pool of melting or molten metal 32 (shown in dotted lines) at the rear of the dished toptof the block 22.

`Above the rear, hearth portion of the copper block 22 the topof the housing 17. is pro-vided with a plurality of orifices or holes 3 6 Vthrough which electrodes extend downwardly. Preferably three electrodes, arranged at the corners of an equilateral triangle are employed and direct current from a suitable power source is Asupplied thereto byany desired known means. However, other kinds ofcurrent, for example three phase alternating current, may be usedif more convenient. vThe number of electrodes and their location and spacing may be varied as required by the size Vof the furnace, Vthe'kind of velectric current used, etc. Y

Each of the electrodes in the embodiment illustrated comprises a hollow body portion 37, a hollow tube 38, preferably concentric with the portion 37, through which cooling liquidrnay be introduced into the latter, and `a refractory tip 39 which may be detachable and replacee able. The electrodes are individually adjustable lin a vertical direction and each is provided with a sealing collar 41 that slidably engages the body 37 and is attached toa nipple 42.extending outwardly around each hole 36. Thefbody portion 37 is preferably of copper andthe tip 39 may be formed of tungsten or other refractory material. Other conditions being xed, contamination of the melt may be minimized by using an electrode tip ofthe same metal as that being fused. It is also possible t use vin place of oneormore or even all of the tubular electrodes shown` consumable electrodes of the same metal as that which is being melted. Such consumable electrodes may be formed of Vcompacted metal sponge and the metalvbath on the hearth portion of the copper block 22 may be replenished by melting of these electrodes.

A feed tube or chute 44 is preferably provided at the rear of the housing Y17. The furnace may be initially charged with metal to be melted through this tube and additional metal may be added therethrough from 'time to time if a consumable electrode or electrodes are not used-or if insuflicient metal is provided by the melting of ysuch electrodes. At its lower end thel tube has an opening 45 through the walls'of the latter into the fusion chamber' 26 above -the hearth portion of the block 22. Thereis also Vprovided on the top of the housing 17 an'upwardly extending tubular Vboss lor nipple 46, vertically aligned with the trough 23 and preferably integral with the housing 17. At the outer end of the boss 46 there is provided a sight-glass 47 of suitable construction through which the openings 2'4-,may be seen `so that the pouring process may be observedand controlled.

The casting chamber 27 which is situated in the housing` 17 below vthe copper block 22 is open on one side to the tunnel 12 and on the other side to the tunnel 13. 'The tunnels are substantially rectangular incross section and may, if desired, be formed integrally with the housing 17, although in many cases it will be preferred to form.

the tunnels separately and secure themeither permanently or detachably to the housing. Each tunnel comprises a floor 51, a front side wall 52, a rear side wall 53, and a top 54.- A pair of spaced, transverse slots 55 are provided in each of the tunnels, the edges thereof lextending 'into' the Vlicor '51, the top 54'and the front side wall 52. Projecting rearwardly from the rear wallf53 Vand `surrounding the Vopen end of each of they slots 575 isa housing 56 that maybe either integral with or detachably Iconnected to the tunnel. j

Gates 58 and 59 are slidably mounted in the two slots passage.

55 of the tunnel 12 and the associated housings 56 and are provided with operating Yrods 61 and 62, respectively, which project from the outer ends of the housings through packing glands 64. Each of the gates 58 and 59 when fully moved into its slot 55, as shown in Figure 1, is effective to close the passage through the tunnel; but when withdrawn into its housing 56 it doesnot obstruct such The rods 61 and 62, respectively, are adapted to move the respective gates 58 and 59 into desired positions. slots 55 and housings 56 and has similar gates 67 and 68 slidably arranged in the slots and housings. The gates 67 and 68, like the gates 58 and 59, are adapted to be moved by their respective operating rods 69 and 70 alternatively to open or close the passage through the tunnel 13. The gates in the tunnels 12 and 13 are provided to establish air locks in the tunnels and thereby prevent access of an undesired atmosphere to the interior of the furnace as the molds 15 are moved into yand out of the casting chamber 27.

Between the gates 58 and 59 inthe tunnel 12 the front wall 52 of the tunnel is provided with an outwardly projecting, semi-cylindrical portion 73. In this and the wall 52, as best shown in Figure l, a cylindrical member 74 is mounted for rotation around a vertical axis. A slot, parallel with the floor 51 of the tunnel 12, is formed through the semi-cylindrical portion 73 and a transverse bore 77 registering therewith is formed in the rotatable cylindrical member 74. A mold push-rod 78, provided with a rounded inner end 79 and agripping member 81 o n its outer end, is associated with the slot in the semi-x cylindrical portion 73 and the Vbore 77.

The rod 78 is longitudinally slidablek in the slot and the bore 77 and by arcuate movement in the slot may cause rotation of the member 74. By imparting to the v pushrod a combination of longitudinal vand arcuate motion thel inner end of the rod may, as shown nFigure 1, be caused to engage each mold 15 as the latter is moved into the space between the gates 5S and 59, and. subsequently, after closing lof the gate S8 and opening of the gate 59, to slide the mold along the floor of the tunnel 12 toward the casting chamber 27. In the embodiment illustrated in the accompanying drawings, the locks formed between the pairs of gates 58, 59 and 67, 68.are made only large enough to accommodate a single mold.

However, it will be understood that if desired the locks,

may be larger so that two or more moldsmay be in-eacll lock atthe same time.

Adjacent the front of the `base plate 16 there is provided a dependingv elevator housing 8.4 which may, if despired, be cast integrally with the base plate. Within the housing S4 there are provided a pair of plungers 86 each of which is slidably mountedtin Athe housing and is furnished at its upper end with an annular 'bevelled portion 8 7. At their lower ends the plungers 8.6 are each provided with a reduced stem 89 by which they aretconnected' to an actuating plate 9.1 movable vertically in the housing 84 and operatively connected to the upper end of a piston rod 92. The latter extends through a packingY glaud'l93 at the lower end of the housingV and-is connected at its other end to a fluid pressure motor 9,4. The .latter may be suspended in any suitable way, as for example by a bracket 96 extending downwardly from the housing 84, and is provided with suitable connections 98 to a source. of pressure fluid.

Nipples 19t) and `1411 extend outwardly from the housing 17. The nipple 1536 has a passage -102communicating with the fusion chamber 26 and the nipple 101 has a passage 103 communicating with the casting chamber 27. A cooling fluid such as water is supplied to and withdrawn -fromrthe passages 29 in the interior of thevr copper block 22 by conduits 105 and 106 which pass through the base plate 16. Glands 107 are provided Vto seal the openings in the base plate through which the conduits 105 and 106'pass.

The molds 15 have substantially the same exterior diam- The tunnel 13 is similarly provided Withapair of eter and height. The mold shown in section in Figure 3 is an investment mold and comprises a shell having a cylindrical side wall 111 connected by a conical portion 112 to a bottom 113 and a cover or cap 116 having an annular centering ring 117 tting within the shell, a conical outer face 118, and a bore 119 therethrough. The shell and the bore 119 of the cap 116 contain investment material 121, of a kind suitable for use in making molds by the well known, so-called lost Wax process, having therein a sprue and a cavity of desired shape, shown in Figure 3 with an impellor blade 122 therein. A portion of the investment material 121 extends above the cap 116 and its periphery is provided with a bevel corresponding to the bevel of the outer face 118 of the cap. The bottom 113 of the mold 15 is provided with an annular groove 123 in which the bevelled projecting portion 87 of one of the plungers 86 may engage to lift the mold lfrom the base plate 16 and carry it upwardly to engage the conical outer surface of the cap 116 and the protruding investment material 121 firmly against the conical wall of one of the pouring openings 24 through the copper block 2.2. Vents 125 are provided from the mold cavity through the investment material 121 and the shell of the mold.

A Variety of investment materials may be used for the molds 15 although it is of course necessary to avoid the use of materials which will readily react with the molten metal or be affected thereby to such an extent that the accuracy of the mold is destroyed. In general, compositions of the types used in making crucibles lfor melting refractory metals such as titanium and zirconium may be used as investment materials. 1t is desirable for the investment material employed to have a relatively high heat conductivity since freezing of the metal will thus be hastened. As a consequence, there is less chance of reaction in the mold and removal of the metal casting within a short time is possible.

A pair of longitudinally movable rods 127 that extend from points in the trough 23 adjacent the openings 24 through the copper block 22 and outwardly through the walls of the housing 17 are provided to dislodge from the mouths of the openings any metal which may be solidified there after filling a mold. Each of the rods 127 may be provided with a handle 128 and there is also provided for each rod an outwardly extending tubular yguide 129 having a sealing gland 131. There are also provided within the casting chamber 27 guide walls 133 for the molds 15. The walls 133 extend upwardly from the base plate 16, with which they may be integral, and are longitudinally aligned with the walls of the tunnels 12 and 13.

The operation of the apparatus above described in producing a plurality of precision castings of a refractory metal is as follows: Initially, air is removed from the interior of the furnace and any molds in the chamber 27. Preferably this is done by rst evacuating the furnace by connecting a vacuum pump to the nipple 101 and, while the passage 162 is closed, withdrawing air through the passage 1113. Flow of an inert gas such as argon or helium is then established through the furnace from the inlet passage 162 to the outlet passage 1113 and such ow is continued. Simultaneously or thereafter the furnace lis tilted about 30 rearwardly, i. e. clockwise from the position shown in Figure 3. The refractory metal or metal and alloying elements in any suitable form, for example pieces of sponge, turnings, powder compacts or loose powder, is then fed onto the hearth portion of the block 22 through the feed tube 44. Electric current is thereupon supplied to the electrodes and an arc is established, the heat of which melts the metal or alloy. Meanwhile flow of cooling liquid through the block 22 and the space between the walls 18 and 19 of the housing 17 has been established and molds 15 have been placed in the tunnel 12 and in the casting chamber 27 below each of the pouring openings 24, the gates in the tunnels 12 and 13 being then closed.

When the metal has become molten, which occurs in only a few minutes, the fluid pressure motor 94 is actuated to raise the molds 15 within the chamber 27 to the positions shown in Figure 3 in which the conical upper surfaces ofthe molds are in close contact with the aring walls of the openings 24 and are held in those positions while the furnace is tilted forwardly (counterclockwise) to a substantially vertical position. The molten metal then runs from the hearth portion of the block 22 into the trough 23 and through the pouring openings 24 into the cavity of the molds. The filling of the molds may be observed through the sight-glass 47. When the molds are substantially filled, and preferably before metal collects above them in the trough 23, the furnace is again tilted rearwardly. Fresh metal may then be admitted through the feed tube 44 to replenish the molten metal bath and while the fresh metal is melting, the molds 15 which have been illed are lowered to position on the base plate 16 and are displaced lfrom the chamber 27 by other unilled molds.

The last mentioned operation will be best understood from Figures l and 2. As previously stated, all of the molds 15 are of substantially the same exterior diameter and height and, accordingly, will occupy the same amount of space in the tunnels 12 and 13 and the chamber 27. The width of the tunnels and the clearance between the guide walls 133 in the chamber 27 are substantially the same as the exterior diameter of the molds so that the molds are maintained in alignment. With the chamber 27 and the tunnels 12 and 13 both lled with the molds as illustrated in Figure 2, the molds in the chamber 27 are displaced by unfilled molds by locking molds into the tunnel 12 and out of the tunnel 13.

Such an operation requires first the opening of the gate 68 and withdrawal of the mold 15 in the outlet lock by suitable tools. The gate 68 is then closed, the gates 67 and 59 are opened, and the mold push rod 78 is actuated manually or by other suitable means to move themold 15 in the lock between the gates 58 and 59 past the gate 59 into the inner portion of the tunnel 12. The path of the push rod handle S1 during operation is indicated by the arrows in Figure l. On being pushed inwardly and swung arcuately, the rod 78 exerts a force on the side of the mold which is thereby caused to slide along the oor 51 of the tunnel toward the chamber 27 until it makes contact with the adjacent mold 15 in the tunnel 12. Then, still under the inuence of the rod 78, the line of molds moves to the right (as viewed in Figure 2) thus pushing another mold into the lock between the outlet gates 67 and 68. Thereupon, the gate 59 is closed. Its closing is followed by closing of the gate 67 and the opening of gates 58 and 63. Another mold is then placed in the lock between the gates 58 and 59 in the tunnel 12, and the mold in the tunnel 13 between the gates 67 and 68 is removed. The gates 58 and 63 are then closed and the process of moving the line of molds by inward and sidewise movement of the mold push rod 7S is repeated. This results in two fresh molds being arranged in the chamber 27 below the pouring openings 24. The fluid pressure motor then is again actuated to raise the molds into pouring position and the furnace is again tilted to ll the molds with molten metal. The foregoing pro cedure is repeated as often as required to cast the desired number of parts.

1t will be evident that admission of air to the interior of the furnace through the tunnels 12 and 13 must be prevented. Accordingly, the lock in each tunnel is provided with a connection 135 through which the air in the lock including `air in the molds may be evacuated after the outer gate thereof is closed and before the inner gate is opened. At other times the connections 135 preferably admit an inert gas to the lock under super atmospheric pressure to prevent air leakage around the outer gates,

The close t between the tops of 'the molds and the copper block-22 during fpouringsubstantially eliminates the possibilityV of metal spilling into the chamber`2f7 and interfering'with movement of the molds. 'In the event that metal 'tends Ito collect and solidify in'the trough 23 above the pouring openings -24, the rods 12"-7 may be pushed inwardly after the furnace is tilted rearwardly-toV normal'position to dislodge any accumulated metal and return it to the pool 3'2 of the molten metal, thus preventing blocking of the pouring openings.

A modied arrangement'for preventing blocking of the pouring openings is shown in Figure 5. 'Here an auxiliary electrode 136 is provided above'each of the pouring openings 24. lf necessary, the electrode 136 may be lowered as indicated b'y" the broken lines arid an arc 'established which Ywill fuse the solidified metal that has collected in the trough 23 above the mold, permitting it either to flow `into a mold or, if the furnace is in rearwardly tilted position during melting of Vthe excess metal, to flow back into the pool of molten metal. Y

'Figure' 4 shows another modification of the invention in which separable, reusable mold blocks are employed. The mold 138 comprises a shell 139, substantially like the shell of the molds 15, that encloses-matching mold blocks '140 (shown with a casting 141V). Above the blocks and extending outwardly from the shell 139 is a pouring tube orsprue 142 having a passage 143 communicating at its lower end with the mold cavity Vandpreferably enlarged at its upper end. As shown in Figure 4, the pouring opening in the copper block22 is somewhat modilied to have a cylindrical neck 147 between the trough 23 and itslower conical portion V148 and the sprue 142 is correspondingly shaped to t snugly in the pouring opening with its upper end substantially ush with the bottom of the trough 23.' lt will be understood, however, that if desired, molds of the type shown in Figure 4 may be formed for use with pouring openings like those shown in'Figures v2,3 and 5. The operation of the furnace with molds of the type shown in Figure 4 is the sarne as hitherto described. The mold blocks 140 and sprues 142 may be formed of any suitable material. Both graphite and copper have been found to give good results since, because of their high heat conductivity, the refractory'metal cools so rapidly that it is not contaminated and the castings may be removed from the molds in a short time, thus permitting the molds to be quickly reassembled for use.

The design of the furnace is such that precision castings of refractory metals and their alloys in intricate shapes may be easily made. In part this results from the fact that when using an atmosphere of an inert gas such `as argon for helium a pressure differential is established between the fusion chamber 26 and the casting chamber 27 when molds are in position for pouring beneath the openings 24. Communication between the chambers is then restricted to that which may be established through the mold cavities and the vents 125 in the molds. When molten metal is caused to ilow into the trough 23y above the pouring openings, passage of inert gas between the chambers 26 and 27 isrcompletely interrupted and the pressure in the chamber 26 will increase, thereby forcing the metal into the mold cavity. It will be observed that such casting by differential pressure does not require auxiliary apparatus or operations, but is "accomplished automatically `as a result of therdesign of the furnace. lt will be further observed that no auxiliary source of pressure fluid to assist in the casting need be provided as the inert gas which provides the protcctive atmosphere durinrY melting and casting of the metal provides all pressure required. The use of an electric arc for melting the refractory metals lalso contributes to the accuracy of the dimensions of the castings since the metal when cast is at a temperature well above the melting point and is hence morefluid.

A large number of castings of titanium, zirconium and alloys 'of both of these metals havebeen made lby the` dimensions wereV very accurate. lThe hardness Yof a number of Vthese-castings lwas compared with the hardness of: the metal or alloy Vbefore melting Vand casting. The comparison showed such slight variations in hardness as to make it evident'that the purity of the metal inthe castings was Vsubstantially unchanged. AThe freedom from contamination of castings producedl by the novel lprocess of the present application has permitted the vaccurate determination of the properties of a number of titanium Aand zirconium Valloys since test specimens of unchanged properties have, been readily formed. Furthermore, the present process has permitted the production of castings'l of thin cross section Afrom such .alloys as: Ti 60`%A1` 40%, Ti 70%-Sn 30%, Zr 90%-Al 10%, and Zr 70%-Sn 30%. These alloys are so brittle that such articles could be formed in no other way.

It will be apparent that numerous variations in and modifications of the process of the present invention and the apparatus described and shown in vthe accompanying drawings may be made without departing from the spirit of the present invention. For example, instead of having the chambers 26 and A27 filled with an inert 'gas during operation, the chambers may be evacuated. As previously pointed out, larger locks may, if desired, be provided in the tunnels. Moreover, the gates forming the locks may be interlocked so as always to maintain the inner gates closedwhile the outer gates are open, and the outer gates closed while the inner gates are open. Further, if desired, the operation of the furnace may be made to a greater or less extent automatic by providing interconnectionsbetween the mold shifting apparatus, the furnace tilting mechanism, and Vthe vmold elevating mechanism. Each of these may also, of course, be modified or changed. It will likewise be apparent that, if desired, the furnace may be designed to make more than the two castings possible in the embodiment illustrated, or only one. Accordingly, it is'to be understood that the invention is not to be considered limited to the precise operation and construction shown' and described, but only by the terms of the appended claims.

As used herein the term their alloys is intended to include not onlyralloys consisting of titanium and zirconium, but 'also alloys of one or both of these metals with other metals.

l. claim: Y

l. A process for making castings of a metal of the group consisting of titanium, zirconium, and their alloys which comprises introducing said metal into a fusion chamber, melting said metal in said fusion chamber on a surface which is not wetted by the molten metal, introducing a mold having a mold cavity into a casting chamber, said casting chamber being below said fusion chamber and communicating therewith, supplying inert gas to said fusion chamber while withdrawing said gas from said casting chamber, movingsaid mold within said casting chamber Vto restrict communication between said chambers, thereby establishing Va pressure differential therebetween, and tilting said surface to introduce molten metal intosaid mo1d,'said mold cavity being in communication with 'both chambers when said mold is in position to restrict communication between said chambers and the sole'communicationV between said chambers when said 'mold is in said position being through said mold cavity.

2. A process as set forth in claim l in which said metal is introduced into said melting chamber without interfering with communication between said chambers.

3.A process for making castings of a metal of the group Vconsisting of titanium, zirconium, and their alloys whichcomprises introducing arnold into a casting chamber, introducing said .metal into afusion-chamber, said fusion chamber .being above said casting `chamber and having an outlet communicating with said casting chamber, melting said metal in said fusion chamber on a surface which is not wetted by the molten metal, intermittently closing said outlet with a mold and by temporarily tilting said surface, lilling said mold with said molten metal, removing the filled mold from said outlet, and subsequently removing said filled mold from position beneath said outlet while simultaneously moving another mold into said position, said melting and casting being carried on in the absence of air.

4. A process for making castings of a metal of the group consisting of titanium, zirconium, and their alloys which comprises introducing a mold into a casting chamber, introducing said metal into a fusion chamber, said fusion chamber being above said casting chamber and having an outlet communicating with said casting chamber, melting said metal in said fusion chamber on a surface which is not wetted by the molten metal, introducing an inert gas into said fusion chamber and withdrawing said gas from said casting chamber, intermittently restricting communication between said chambers by closing said outlet with a mold, filling said mold with said molten metal through said outlet by temporarily tilting said surface while said outlet is so restricted, removing the filled mold from said outlet, and subsequently removing said filled mold from position beneath said outlet while simultaneously moving another mold into said position.

5. A process as set forth in claim 4 in which the pressure of said inert gas is utilized to assist in forcing said molten metal into said mold.

6. In apparatus for making castings of a metal of the group consisting of titanium, zirconium and their alloys, a tiltable furnace comprising a housing, a melting hearth in said housing and tiltable therewith, means for melting a metal on said hearth, said hearth being shaped to provide a portion adapted, in one position of said furnace, to hold molten metal and to provide a downwardly directed pouring opening through which, in another position of said furnace, molten metal may ow, a mold chamber in said housing, said chamber being formed in part by said hearth, and a mold in said chamber beneath said pouring opening adapted to receive molten metal, said housing being adapted to exclude air and having an inlet and an outlet adapted to allow ow of an inert gas therethrough.

7. Apparatus as set forth in claim 6 in which said hearth is provided With a passage for circulation of coolant.

8. In apparatus for making castings of a metal of the group consisting of titanium, zirconium, and their alloys, a tiltable furnace comprising a housing, a partition in said housing dividing the interior of said furnace into an upper chamber and a lower chamber and having an opening providing communication between said chambers, means for melting said metal in said upper chamber on a portion of said partition, a mold in said lower chamber adapted to be filled through said opening with molten metal when said furnace is tilted in one direction, and means for removing said mold from its position in said lower chamber and simultaneously moving another mold into the same position.

9. Apparatus as set forth in claim 8 in which means is provided for supplying empty molds to said lower chamber and removing lled molds from said lower chamber without admitting air to said housing.

10. Apparatus as set forth in claim 8 which further comprises an inert gas inlet into said upper chamber, an inert gas outlet from said lower chamber and means for raising said mold into contact with said partition during filling thereof.

11. Apparatus as set forth in claim 8 in which means is provided for removing metal obstructing said opening.

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3. A PROCESS FOR MAKING CASTINGS OF A METAL OF THE GROUP CONSISTING OF TITANIUM, ZIRCONIUM, AND THEIR ALLOYS WHICH COMPRISES INTRODUCING A MOLD INTO A CASING CAHMBER, INTRODUCING SAID METAL INTO A FUSION CHAMBER, SAID FUSION CHAMBER BEING ABOVE SAID CASTING CHAMBER AND HAVING AN OUTLET COMMUNICATING WITH SAID CASTING CHAMBER, MELTING SAID METAL IN SAID FUSION CHAMBER ON A SURFACE WHICH IS NOT WETTED BY THE MOLETN METAL, INTERMITTENTLY CLOSING SAID OUTLET WITH A MOLD AND BY TEMPORARILY TILTING SAID SURFACE, FILLING SAID MOLD WITH SAID MOLTEN METAL, REMOVING THE FILLED MOLD FROM SAID OUTLET, AND SUBSEQUENTLY REMOVING SAID FILLED MOLD FROM POSITION BENEATH SAID OUTLET WHILE SIMULTANEOUSLY MOVING ANOTHER MOLD INTO SAID POSITION, SAID MELTING AND CASTING BEING CARRIED ON IN THE ABSENCE OF AIR.
 6. IN APPARATUS FOR MAKING CASTINGS OF A METAL OF THE GROUP CONSISTING OF TITANIUM, ZIRCONIUM AND THEIR ALLOYS A TILTABLE FURNACE COMPRISING A HOUSING, A MELTING HEARTH IN SAID HOUSING AND TILTABLE THEREWITH, MEANS FOR MELTING A METAL ON SAID HEARTH, SAID HEARTH BEING SHAPED TO PROVIDE A PORTION ADAPTED, IN ONE POSITION OF SAID FURNACE, TO HOLD MOLTEN METAL AND TO PROVIDE A DOWNWARDLY DIREACTED POURING OPENING THROUGH WHICH IN ANOTHER POSITION OF SAID FURNACE, MOLTEN METAL MAY FLOW, A MOLD CHAMBER IN SAID HOUSING, SAID CHAMBER BEING FORMED IN PART BY SAID HEARTH, AND A MOLD IN SAID CHAMBER BENEATH SAID POURING OPENING ADAPTED TO RECEIVE MOLTEN METAL, SAID HOUSING BEING ADAPTED TO EXCLUDE AIR AND HAVING AN INLET AND AN OUTLET ADAPTED TO ALLOW FLOW OF AN INERT GAS THERETHROUGH. 